Pivotal cam plate mechanism



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United States Patent 6 PIVOTAL CAM PLATE MECHANISM Sherman Z. Dushkes,Redwood-City, and George I. Willey, Vallejo, Calif.

Application August 2, 1954, Serial No. M73449 Claims. (Cl. 74-41%)(Granted under Title 35, U. S. Code (1952), sec. 266) This invention,which relatesto driving connections and more particularly to cammechanisms for converting bidirectional input motions intounidirectional output motions, may be manufactured. and used by or fortheGovernment of the United States of America for governmental purposeswithout the. payment of any royalties thereon or therefor.

lnamaking certain driving connections, it sometimes becomes necessary toprovide a linkage capable of coner-ting av longitudinally bi-directionalmotion produced by a driving member into a unidirectional motion in adirection that is transverse to. this longitudinal drive. Morespecifically, the linkagerequirement may be one in which the drivenmember always is to. be moved only to one. side of. a neutral. position.even though the driving member producing this motion is moved on bothsides of thatneutral position.

Thus, by way of. example, the flow ratio controller in the. errorchannelof a pressure demand servomechanism usually requires a metering valvein. the hydraulic bypass circuit and 4-way valve-metering valve unit inthe hydraulic load circuit. The bypass metering valve stem movement thatcontrols the valve port area is produced through a mechanical drivingconnection or. linkage with the 4-way valve-load metering valve unit.The 4-way valve-load metering valve unit accomplishes its opening andclosing movements on either side of a neutral position. in response to.increasing and decreasing servomechanisrn error signals in the positiveand negative directions. Consequently the valves of this unit have whatcan be called bi-directional movement (movement to either side) fromthis neutral position. However, the by-pass metering valve: accomplishesits closing and opening movement-s only to one side of its neutralposition. in response to increasing and decreasing servornechanism errorsignals in Consequently, this valve should have whatcan becalledunidirectional movement (movement to one side). from this neutralposition.

The requirement then is to convert the bi-directional movement of thedriving member (4-way valve-load metering valve) into a unidirectional.movement in the driven member (by-pass metering valve) and, one of thebetter known linkages for accomplishing this conversion is. theso-called V-block cam mechanism. In making such a linkage the V-blockcam plate may be secured for reciprocation with the valve stem of the4-way valveload metering valve unit, while the usual cam follower ismounted on the by-pass metering valve stem, and, with such a coupling,it should be clear that, if the neutral position of the by-pass meteringvalve is one in which the valve stem follower contacts the notch of theV- block, then bi-directional reciprocation of the block will effectlinear displacements of the follower and its valve stem in amountsproportionate to the bi-directional displacements but to one side onlyof the neutral position.

Although such V-blocks are fully effective insofar as producing thedesired action, they nevertheless are undesirable in many installationsdue to the fact that, if the ice block is moved rapidly through centerposition, thereis:

curving of the V-notch, but such a modification hasvthc' obviousill-effect of sacrificing functional precision since the desiredrelation between input. and output motion then is altered under allconditions of operation. Inthemetering valve problem stated earlier,another possiblesolution could be the use of a two-valve system in placeof the single bypass metering valve,.and, although this duplicatoryprocedure might be operable, it is objectionable because of its spacerequirements and also its need for precise duplication if the input andoutput relation is to be exact. Other proposals have been made but,sofar as is presently known, the various attempts to reproduce theV-block cam action have resulted. in unduly complicated arrangementswhich are most impractical for many purposes.

As will be recognized, the above-described use of the V-block cammechanisms and their equivalents to control a by-pass metering valve isonly one of the many possible instances in which the V-block action isdesirable. In the same manner, thereare many other-instances orpossibilities for use of i the invention about to be described.

As to the present invention, one of, its primary objects is to provide acam mechanism capable of reproducing the action of the. describedV-block cam mechanism and: also capable of prolongating its operationallife by the relative elimination of fatigue failures produced byacceleration shocks.

Another object is to accomplish aprecise reproduction of the action ofthe V-block cam mechanism in a simple. manner capable of being performedby a small compact apparatus.

These and other objects. will be: apparent from the detailed descriptionand accompanying drawings;

In the present invention these objectives are accomplished basically bythe use of pivotal member in place of the V-block, this member being apivotally mounted cam plate upon which a cam follower is brought tobearin such a manner that reciprocation ofthe plate transversely 0a thefollower causes the plate to pivot; aboutits axis. Further, in thepreferred form, the plate is centrally pivoted and the pivotal action iscontrolled by stops to; the extent that. successive swings in oppositerotational directions about the axis automatically reproduces theangular relationship of the legs. of the V-block. In. such anarrangement, the reciprocating cam plate may be connected to thebi-directional input so as to constitute the driving member, While thecam follower may be carried by a valve stem which then becomes a drivenoutput member capable of operating a uni-directional valve, or the like.Most suitably, the f'olloweris a roller and, also, the cam plate ispivotally mounted on a carriageprovided with a tracking surface engagingthrust bearings. It also is desirable in order to provide a preciselinear relationship between the displacements of the cam plate and thefollower to assure that the radius of the roller follower and thepivotal radius of the cam. plate are made equal.

In such a mechanism, it should be rather apparent that not only is theV-block action duplicated but, of equal importance, the action issuchthat the swing or pivoting imposes a slight delay or lag during theinterval that the roller follower moves through center position, such alag being beneficial insofar as shock reduction is concerned. Thus, ineffect, the action is similar to that which might be accomplished if theV-block were provided with an arcuate notch, although, at the same time,the inputoutput relationship of the V-block is maintained. It also willbe clear that the stops can be varied in accordance with the job to beperformed, so that the arrangement can be made to reproduce the actionsof V-blocks of varying angles or, in fact, the cam surfaces can besomewhat curved to produce whatever output position characterization maybe deemed desirable.

The preferred embodiment of the invention is illustrated in theaccompanying drawings of which Fig. 1 is a plan view of the cammechanism connected to fluid valves, and Fig 2 a longitudinal sectiontaken along lines II-II of Fig. 1.

Referring to the drawings, the cam mechanism, generally indicated bynumeral 2, is connected at one end to a stem 4 ofan input device, suchas a valve (not shown), input being transmitted through a coupling toanother stem 6 of an output device that may be a bypass metering valve8. The input and output devices, most suitably, are fixed on a support 9over which the cam mechanism reciprocates and, in the illustratedembodiment, the cam mechanism functions to translate a bidirectionalsignal input to a uni-directional linear output motion in valve 8 forcontrolling the by-pass of the fluid between lines10 and 12. Aspreviously mentioned, such valves are shown for explanatory purposesonly and it should be obvious that the cam mechanism may be used inother servomechanisms,regulators, machine tools, computers, etc.

Considering the cam mechanism in further detail, it may be seen toinclude an elongate cam plate 14 that is intermediately pivoted on areciprocable carriage 16, the

pivotal action of the plate being influenced by a cam follower formed,preferably, of a pair of rollers 17 mounted on a valve stem 6 andresiliently urged by spring 19 against plate 14. These rollers orfollowers are carried by pins 18 which, in turn, are secured to oppositesides of an alignment block 20, this block being threaded to stem 6 andalso extending through a longitudinal slot 21 in the plate to maintainthe rollers in alignment with the cam tracks. The longitudinal positionof stem 6 may be adjusted by loosening lock nut 22 and rotating thestem. However, this structure can be simplified by the use of a dog setscrew for guiding stem 6, such a screw making it possible to eliminatethe slot in the cam as well as one of the cam followers. In the eventthe dog set screw is utilized, other suitable mechanical means can beprovided to adjust stem 6. Adjustable stop 23 is provided with a crossbar positioned in the path of the valve stem as a safety precaution toinsure that cam plate 14 rotates from one angular position to the otheras the mechanism passes through center. Since clearance is at all timesprovided between stop 23 and the end of stem 6, the stem will strike thestop only in case cam plate 14 freezes or fails to rotate due, forexample, to high bearing sticking resistance. Asa further structuralfeature, it is to be noted that the cam plate is provided medially withspaced lugs or ears 24 extending laterally from the cam track andprovided with bearing surfaces for receiving pins 25 and bearings 26 onwhich the plate as a whole is pivotally supported, the cam plate beingpositioned between spaced upper and lower carrier sections which form acam cage. Preferably, cam plate 14 is adjustable through rotation ofpins 25 for aligning slot 21 with respect to block 26.

Carriage 16 is connected to the input device through turnbuckle 27 (Fig.1), the carriage being reciprocable transversely of output stem 6 andslidable on a shim plate 28 bolted to support 9. To guide thereciprocable motion of the carriage and take up the transverse thrustarising from the spring-loaded cam followers, a guide bracket St? isbolted to support 9 and is provided with a pair of spaced rollers 32slidable along flat upper and lower carrier surto and balanced with camfollower rollers 17.

Cam plate 14 is shown in the drawing as being in its central or neutralposition and as there seen the pivotal axis of the cam and therotational axis of the cam followers 17 are aligned. However, insofar asthe mutual relationship of these members is concerned, the importantfeature is that the rotational radius of the cam followers be equal tothe pivotal radius of the cam plate, such a relationship assuring asmooth translation of movement between the input and output. In thisrespect, it will be apparent that any substantial variation in theseradii would product a jump or discontinuity in the output movement atthe time that the plate rotates.

In its neutral position, it will be realized that customarily the camplate will be swung in one or the other directions and the amount of itsswing can be controlled by stops 36 which may be integrally formed onthe carrier sections. The amount or angle of the swing can be varied asdesired, the swing represented in the drawings being one of 45.Preferably, a rubber bumper 38 is inset on the surface of the camadjacent each stop for absorbing shock and reducing noise, and, ifneeded, such bumpers also can be included in the stops. When the carrieris displaced from the illustrated neutral position by the input device,the spring force of the followers applies a torque to the cam and if thecam has not been previously displaced to its designated limit position,the applied torque will cause the cam to rotate and assume such aposition, the particular limit position depending, of course, upon thedirection of the carrier displacement from neutral. With the mechanismillustrated, it has been found that a carrier movement of .005 inch willprovide sufficient torque to induce rotation of the plate. As thecarrier is moved away from neutral in either direction, the pivot pointof the cam is offset from the axis of the cam followers and thefollowers, being spring-pressed against the cam, ride along the inclinedsurface moving valve stem 6 an amount proportionately equal to thecarrier displacement and, of course, the direction of output movementwill be the same regardless of whether the carrier is displaced to oneside or the other of the neutral position.

One important advantage of the cam mechanism arises as the carrier ismoved rapidly from a position on one side of the center to a position onthe other side. Thus, during this travel there is a minute time delay asthe cam swings from one limit position to the other in passing throughthe center position. This dela, however, is sufficient to permit thefollower to decelerate before changing its direction of movement. Asaconsequence, this pivotal feature with its time delay materiallyincreases the life of the cam mechanism by reducing shock whichotherwise would cause eventual fatigue failure when the cam followersare rapidly accelerated through neutral position. Such durability, ofcourse, is a particularly important consideration in servomechanismswhere reliable response is necessary for long periods of time withoutopportunity for normal maintenance. Further, it will be appreciated thatthe particular mechanism is unusually simple and easily adjustable, sothat the complications arising upon earlier attempts to reproduce theV-block action are eliminated.

Obviously, many modifications and variations of the present inventionare possible in the light of the above teachings. It is, therefore, tobe understood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

We claim:

1. Pivotal cam mechanism comprising a reciprocable carrier, a cam platepivotally mounted on the carrier, a cam follower reciprocable toward andaway from said plate, and means urging said follower toward the plate,said follower engagement causing said earn plate to pivot during saidcarrier reciprocation.

2. Pivotal cam mechanism comprising a reciprocable carrier, a cam platepivotally mounted on the carrier, a cam roller follower reciprocahletoward and away from said plate, and means urging said follower towardthe plate, said follower engagement causing said cam plate to pivotduring said carrier reciprocation for imparting movement to saidfollower, said cam plate being spaced from its pivotal axis a distanceequal to the rotational radius of said cam roller.

3. Pivotal cam mechanism comprising a reciprocable carrier, a camcentrally pivoted on the carrier, stops mounted on the carrier on eachside of the pivot point of the cam for limiting the angular displacementof the cam, a stem reciprocable toward and away from said cam, a rollercam follower mounted on said stem, means mounted on the stem urging saidstern and follower toward the cam, and means for reciprocating thecarrier trans versely of said stem whereby a motion imparted to the camin one direction will be transmitted to the follower in anotherdirection.

4. Pivotal cam mechanism comprising a reciprocable carrier, a camcentrally pivoted on the carrier, a stem reciprocable toward and awayfrom said cam, a roller 6, cam follower mounted on said stem, meansurging said stem and follower toward the cam, means for guiding the camfollower along the cam, and means for reciprocating the carriertransversely of said stem whereby a motion imparted to the cam in, onedirection will be transmitted to the roller in another direction.

5. Pivotal cam mechanism comprising a reciprocable carrier, an elongatecam plate centrally pivoted on the carrier, a stern reciprocable towardand away from said cam, a roller cam follower mounted on said stem,means urging said stern and follower toward the cam plate, and means forreciprocating the carrier transversely of said stem whereby a motionimparted to the cam in one direction will be transmitted to the rollerin another direction, said cam plate being spaced from its pivotal axisa distance equal to the rotational radius of said cam roller AbramsonJuly 29, 1930 Manhartsberger Mar. 7, 1950

